Like Atticus, Alexandra stands by what she believes in. Unlike Atticus, Alexandra believes the most important things in life are related to family and protecting your own.
Atticus stands up for his cause and his values by defending Tom Robinson (among other things) and Alexandra stands up for her values vocally in her protective treatment of Atticus, Jem and Scout.
Alexandra is obsessed with her family heritage, and she believes that few (if any) families in Maycomb are equal to the Finches. She believes in Family Streaks, Fine Folks and gentle breeding: The Finches are Fine Folks and a product of gentle breeding (which Atticus can't quite explain to Scout), but in Alexandra's mind, her family is immune from the streaks--drinking, gambling, meanness--from which every other family suffers. Alexandra prevents Scout from playing with Walter Cunningham Jr. because she considers his family "trash"; but she learns a lesson herself at the Missionary Circle tea when the pious Mrs. Merriweather turns on Alexandra, criticizing Atticus for his decision to defend Tom Robinson while she eats the food he has provided under his own roof.
The Finches all show a capacity to learn and mature. Atticus is obviously an educated, thoughtful man. Scout loves to read even if she dislikes school. Jem matures as the story progresses, learning some valuable lessons he may not have anticipated learning but accepting them when they do arrive.